This invention relates to pedal-type driving devices, particularly such devices suitable for bicycles, and bicycles equipped with these driving devices.
It is well known that standard bicycles are driven using foot operated pedals that are able to turn, by means of a crank arrangement, one or more chain sprockets that are rotatably mounted on the bicycle frame. A continuous chain extends from the chain sprocket or one of the chain sprockets to a chain sprocket mounted at the rear wheel axle. In many cases, there may be a plurality of chain sprockets of different sizes at the rear wheel axle and a gear changing mechanism is provided for moving the chain from one of the sprockets to another. A number of proposals have been made in the past for improving the operational performance of a bicycle by varying the effective length of the crank arm to which each pedal is attached. If the effective length of the crank arm can be increased during the downward stroke phase of each pedal, then the amount of rotational torque applied to the driving chain sprocket with the same amount of exertion or work by the bicycle rider is also increased. However, as far as the applicant is aware, these prior attempts to vary the length of the crank arm attached to each pedal have not met with commercial success, possibly due to mechanical inefficiencies or problems.
One recent patent which teaches a variable length crank arm for a bicycle is U.S. Pat. No. 5,879,017 which issued Mar. 9, 1999 to J. N. Debruin. In this known bicycle drive, the crank arms or crankshafts are secured to opposite ends of an existing sprocket shaft of the bicycle. Each crankshaft has an elongated slot extending a length thereof and has a sliding bearing coupled with an upper end thereof. Each sliding bearing has a roller disposed on a rear surface thereof and the two rollers are coupled with a pair of circular races which in turn are coupled with the existing sprocket shaft. The pedals are mounted within the elongated slots of the crankshafts and they are attached by shaft portions to the sliding bearings.
U.S. Pat. No. 6,152,471 which issued Nov. 28, 2000 to Byung Nam Kang et al. teaches two different versions of a variable pedal driving device for a bicycle. A main drive shaft extends through a short shaft pipe. Two power transmission units and crank shafts are respectively installed on opposite ends of the main shaft. The two pedals are mounted on respective, hollow slide members which are slidable along respective crankshafts. Rotary levers are attached by means of shafts to respective slide members. One end of each power transmission unit is fixedly connected to the shaft pipe so as to extend radially therefrom. The power transmission units each include a sprocket which is connected to another sprocket by means of a continuous chain. With this arrangement, when each pedal is driven in the forward direction, the crankshaft is caused to extend out to a maximum distance from the main shaft to provide more efficient transmission of foot power to the bicycle.
It is an object of the present invention to provide an improved pedal-type driving device which can be used to drive a wheeled vehicle such as a bicycle and which is reliable and easy to use.
It is a further object of the present invention to provide an improved pedal-type driving device which employs two power transmission units, one at each end of a main drive shaft with each unit including a planetary sprocket, a pedal, and a crank arm connecting the pedal to the sprocket wherein each power transmission unit allows the distance of the pedal from the central axis of the main shaft to vary substantially as the pedals are moved about the central axis during use of the driving device.
According to one aspect of the invention, a driving device includes a main shaft having first and second ends and rotatable about a main central axis thereof and a chain sprocket co-axial with the main shaft and mounted for rotation with the main shaft, the chain sprocket being adapted to drive a continuous drive chain. There are also two power transmission units, each of which is mounted at a respective one of the first and second ends of the main shaft, with each power transmission unit including an elongate crank having a predetermined, fixed length, a pedal attached to the crank at a fixed location at an outer end of the crank, a flexable continous drive member, a planetary sprocket fixedly attached to an opposite end of the crank for movement therewith and operatively connected to the continuous drive member. The planetary sprocket has a central axis which is substantially parallel to the main central axis but spaced therefrom. This sprocket is rotatable in an orbit around the main central axis upon movement of its respective pedal. There is also a non-rotating sprocket coaxial with the main shaft and operatively connected to the continuous drive member. The distance of each pedal from the main central axis is varied by its respective power transmission unit as each pedal is moved about the main central axis.
Preferably, each power transmission unit includes a rotatable sprocket supporting member on which the planetary sprocket is mounted for relative rotation therewith and one of the sprocket supporting members is fixedly connected to one side of the chain sprocket. Furthermore, in an preferred embodiment, each pedal is fixedly and non-rotatably connected to its respective crank member.
According to another aspect of the invention, a pedal-type driving device suitable for a bicycle includes a main shaft having first and second ends and rotatable about a central axis thereof and a chain sprocket adapted for mounting about the main shaft in a coaxial manner for rotation therewith. The chain sprocket is engageable with a chain to drive a driving wheel of the bicycle. There are also two power transmission units, each of which is mounted at a respective one of the first and second ends of the main shaft. Each transmission unit comprises a non-rotating first sprocket connectable to an adjacent support structure of the bicycle during use of the driving device, a rotatable, planetary second sprocket spaced radially outwardly from the first sprocket, a pedal, a crank connecting the pedal to the second sprocket, and a flexible, continuous drive member extending around and between the first and second sprockets and adapted to rotate the second sprocket when the attached pedal is rotated about the main shaft. In addition, a sprocket supporting member is fixedly attached to a respective one of the ends of the main shaft and is attached to and supports the second sprocket so as to allow rotation of the second sprocket relative to the supporting member. The chain sprocket is adapted for mounting on one of the power transmission units for rotation with the sprocket supporting member of the one power transmission unit. The distance of each pedal from the central axis varies substantially as the pedals are moved about the central axis during use of the driving device. The pedals and their attached cranks are able to provide greater rotational torque to the main shaft during a driving phase of the rotation when the pedals are at a greater distance from the central axis.
In a preferred embodiment, the sprocket supporting member of one of the transmission units is connectable by threaded fasteners to one side of the chain sprocket. Preferably, the sprocket supporting member is a relatively flat housing that surrounds its respective continuous drive member and the first sprocket.
According to still another aspect of the invention, there is provided a foot-powered, wheeled vehicle having a support frame, a steerable front wheel, and at least one, driven rear wheel connected to at least one driven sprocket for rotation therewith. A main drive shaft is rotatably mounted in the support frame and has first and second ends. A chain sprocket coaxial with the drive shaft is mounted for rotation with the drive shaft. A continuous chain extends between and operatively connects the chain sprocket and the at least one driven sprocket. The improvement in this vehicle is the use of two power transmitting devices, each of which is mounted at a respective one of the first and second ends of the drive shaft. Each of these power transmitting devices includes an elongate crank member having a fixed length, a pedal attached to the crank member at a fixed location at an outer end of the crank member, and a sprocket fixedly attached to an opposite end of the crank for movement therewith. The sprocket has a central axis of relative rotation which is substantially parallel to a central axis of the main drive shaft but is spaced therefrom. This sprocket is rotatable in an orbit around the central axis of the main drive shaft. When the vehicle is driven, the distance of each pedal from the central axis of the main drive shaft is varied by its respective power transmission device as the latter is rotated by its pedal and reaches a maximum distance during a downward stroke of the pedal.
In a preferred embodiment of this vehicle, the power transmitting device includes a continuous timing belt which extends around and is operatively connected to the sprocket and a non-rotatable, second sprocket that is co-axial with the main drive shaft and that is fixedly connected to the support frame.
Further features and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings.